Reopening date is the date when issue's resolution field changes from a value to EMPTY.
To create a First/Last Reopened date custom field
- Navigate to JIRA Admin > Add-ons > Enhancer Plugin Menu > Custom Field Configuration and switch to Date tab.
- Click on button.
- Fill the dialog
- Pick JEP - First Reopened Date or JEP - Last Reopened Date in custom field drop down.
- Give a name to the custom field
- And click Add Custom Field button. That's it.
This custom field can be used to sort or search in issue navigator.